The present invention relates to cutting inserts, a method of assembling the cutting inserts on a cutter body, and the assembled cutter body.
Depicted in FIGS. 1 and 2 is a conventional milling cutter comprising a rotatable holder body 1 having a plurality of circumferentially spaced insert seats 2. Mounted in the insert seats are indexible cutting inserts 3 with optional shims 4. The inserts 3 and shims (if provided) are held in place by fastening screws 5 that extend through holes formed in the inserts and the shims. The fastening screws are threadedly attached in threaded holes 6 that are formed in support surfaces 7, the holes 6 extending perpendicularly to the respective surfaces 7. Such a milling cutter is disclosed, for example, in U.S. Pat. No. 5,871,309.
In order to tighten the screws, it is necessary to insert a turning tool into a cavity formed in the screw head. From FIG. 2 it will be appreciated that the center axis A of the screw nearly intersects a radially outer edge 10 of a surface 12 of a pocket 14 that is formed in front of each insert seat 2. That hampers the insertion of a turning tool and requires that special turning tools with long shanks be used to avoid interference of the edge 10 with the tool""s handle.
Therefore, it would be desirable to provide a cutting insert mounting arrangement having a fastening screw that is not only readily accessible, but which makes 360 degree contact with the wall of the insert""s through-hole while urging the insert simultaneously rearwardly against a supporting surface and laterally against an abutment surface.
Furthermore, it is desirable to secure a cutting insert as snugly as possible in its respective seat so that the insert will not vibrate or chatter. A typical seat possesses not only a rear support surface in which the treaded screw-receiving hole, but also an upstanding abutment surface. By pressing the insert against both the rear support surface, and the abutment surface, the insert is more stabilized and less prone to vibrate or chatter. Various ways have been proposed to enable a fastener screw to press the insert in that manner. For example, as disclosed in U.S. Pat. No. 6,053,671, a fastener screw can be inserted into a threaded hole extending perpendicularly into the support surface, but positioned relative to the abutment surface whereby one portion of a head of the screw will push the insert not only rearwardly against the supporting surface, but also laterally against the abutment surface.
Another technique, disclosed in U.S. Pat. No. 3,662,444 involves orienting the threaded hole non-perpendicularly relative to the supporting surface. Then, when the fastener screw is inserted through the center through-hole of the insert and into the threaded hole, a conical surface on the screw head will bias the insert rearwardly against the supporting surface, and laterally against the abutment surface.
A shortcoming associated with the arrangements described in U.S. Pat. Nos. 6,053,671 and 3,662,444 is that the screw head makes contact with the wall of the insert""s through-hole for less than 360 degrees, thereby limiting the amount of stabilization of the insert that can be achieved.
Disclosed in U.S. Pat. No. 5,199,828 is a mounting arrangement for a turning insert which enables the insert to be exchanged without removing the fastening screw. To accomplish that, the center hole formed in the insert has a larger maximum cross section than the head of the screw. In order to enable the screw head to secure the insert in place, the axis of the screw is tilted relative to the axis of the center hole, whereby the screw enters the rear support surface at an oblique angle. That inherently results in the insert being pushed against the abutment surface by the screw head. The screw head contacts the wall of center hole at two diametrically opposed locations, i.e. the contact between the screw head and the insert is non-continuous, so insert stability is not maximized.
The present invention relates to a cutting assembly, a method of mounting a cutting insert to a tool holder of the assembly, and to the insert per se.
The cutting assembly comprises a tool holder which has an insert seat. The insert seat includes a seat surface into which a screw-threaded mounting hole extends in a direction obliquely to a plane of the seat surface. A cutting insert is mounted in the seat. The insert has a front surface and a rear supporting surface oriented parallel to the seat surface. The insert has a through-hole defining a center axis and including a front cavity disposed at the front surface of the insert. The front cavity is defined by a wall, at least a screw-supporting portion of which has a circular cross-section and tapers toward the rear supporting surface. A fastening screw extends through the through-hole and includes a threaded shank, and an enlarged head which is disposed in the cavity. The head includes an outer face configured as part of a sphere which makes 360 degree contact with the screw-supporting surface of the cavity wall. The threaded shank is threadedly mounted in the mounting hole. The head and shank are shaped symmetrically about the center axis of the screw. The center axis of the screw forms an acute angle with the center axis of the through-hole.
Preferably, the insert seat includes an abutment surface extending outwardly from the seat surface, the screw-mounting hole oriented so that the screw applied to the insert a force having a component directed toward the abutment surface.
Preferably, the center axis of the screw extends forwardly from the screw in the direction of rotation and diverges from the center axis of the through-hole in a direction away from the axis of rotation.
The invention also pertains to the method of mounting the cutting insert to the insert seat.
The invention also pertains to the cutting insert per se.